The present application claims priority from Japanese Patent Application No. 2014-249905, filed Dec. 10, 2014, which is incorporated herein by reference.
The present invention relates to an air leading type two-stroke engine and an intake system for the same, and a carburetor.
Two-stroke engines are used as portable working machines such as brush cutters, chain saws and power blowers (JP Patent Laid-Open No. 11-9051). As well-known, two-stroke engines are supplied with mixed fuel including gasoline containing oil. In this type of two-stroke engine, an intake system includes a carburetor. As carburetors, those using a butterfly valve and those using a rotary valve (U.S. Pat. No. 7,261,281 B2) are known. Carburetors including a rotary valve are called “rotary type carburetors”.
In development of two-stroke engines, efforts for compliance with environmental regulations have been made. Typical examples of such engines are air leading type two-stroke engines (U.S. Pat. No. 6,962,132 B2 and International Publication No. WO 98/57053).
In an air leading type two-stroke engine, at an initial stage of a scavenging process, air is induced to a combustion chamber, and subsequently, an air-fuel mixture in a crankcase is induced to the combustion chamber. This type of engine includes a scavenging channel that communicates with each of a combustion chamber and a crankcase. Air is charged to the scavenging channel from an upper portion thereof. In an air leading type two-stroke engine, at an initial stage of a scavenging process, air accumulated in the scavenging channel is induced to the combustion chamber. Scavenging is performed using the air, providing the advantage of being able to reduce HC components in gas emissions.
U.S. Pat. No. 6,962,132 B2 discloses a fundamental configuration of an intake system in an air leading type two-stroke engine. Here, as can be understood from FIG. 1 in U.S. Pat. No. 6,962,132 B2, an intake system in an air leading type two-stroke engine means a route from a filter element of an air cleaner to an engine body.
A fundamental configuration of the intake system in the air leading type two-stroke engine includes two passages. One of the passages is an air passage that allows air to be supplied to a scavenging channel in the engine. The other passage is an air-fuel mixture passage that allows mixed fuel containing oil to be supplied to the engine.
U.S. Pat. No. 6,962,132 B2 discloses an intake system including a throttle valve in a two-stroke engine. Upon the throttle valve being brought to a full-open position, in the engine of U.S. Pat. No. 6,962,132 B2, the air passage from the filter element to the engine body and the air-fuel mixture passage from the filter element to the engine body become independent individually.
As air leading type engines, a piston valve type engine that uses a piston in order to control air to be supplied to a scavenging channel (International Publication No. WO 98/57053 and U.S. Pat. No. 7,513,225 B2, U.S. Pat. No. 6,857,402 B2) and a lead valve type engine that uses a lead valve in order to control air to be supplied to a scavenging channel (JP Patent Laid-Open No. 10-121973) are well-known. Here, U.S. Pat. No. 7,513,225 B2 discloses an intake adapter interposed between a carburetor and an engine body. The intake adapter includes an air channel and an air-fuel mixture channel. The air channel and the air-fuel mixture channel are formed by dividing an internal passage of the intake adapter by means of a partition wall.
U.S. Pat. No. 7,494,113 B2 discloses a carburetor to be employed in an air leading type two-stroke engine. The carburetor includes a throttle valve, a choke valve and a partition member positioned between these valves. Each of the throttle valve and the choke valve is comprised of a butterfly valve. U.S. Pat. No. 7,494,113 B2 proposes a carburetor using the aforementioned partition wall, the carburetor enabling easy assembling of the carburetor.
FIG. 4 in U.S. Pat. No. 7,494,113 B2 discloses a carburetor including two half partition members positioned oppositely to each other. The two half partition members are spaced from each other at a center area of a gas passage in the carburetor. An opening formed by the opposite ends of the two half partition members, substantially provide a communication portion that brings the air passage and the air-fuel mixture passage into communication with each other in the intake system in the air leading type engine.
FIGS. 63 to 65 attached here are schematic diagrams of the carburetor disclosed in FIG. 4 in U.S. Pat. No. 7,494,113 B2. In FIGS. 63 to 65, reference numeral 400 denotes a gas passage in the carburetor. In the gas passage 400, a choke valve 402 and a throttle valve 404 are disposed. The throttle valve 404 is positioned on the downstream side of the choke valve 402. Reference numeral 406 denotes a rotation shaft of the choke valve 402, and reference numeral 408 denotes a rotation shaft of the throttle valve 404.
Between the choke valve 402 and the throttle valve 404, two half partition members 410 are disposed. Each half partition member 410 is comprised of a flat plate. The opposite ends of the two half partition members 410 form an opening 412 at a center area of the gas passage 400 in the carburetor. The opening 412 substantially provides the “communication portion” that brings the air passage and the air-fuel mixture passage in the air leading type engine.
FIGS. 63 to 65 illustrate the choke valve 402 in a full open position and the throttle valve 404 in a full open position. Between the choke valve 402 and the throttle valve 404, the half partition members 410 are positioned. The flat plate-like half partition members 410 partition a part of the opening 412 between the choke valve 402 in the full open position and the throttle valve 404 in the full open position. Consequently, the half partition members 410 form two channels 414 and 416 (FIG. 64) in the gas passage 400, jointly with the choke valve 402 and the throttle valve 404, which are both in the fully-open positions.
The first channel 414 is an air channel through which air passes, and provides a part of an “air passage” in the intake system of the air leading type engine. The second channel 416 is an air-fuel mixture channel for producing an air-fuel mixture, and provides a part of an “air-fuel mixture passage” in the intake system of the air leading type engine.
Air to be supplied to the scavenging channel of the two-stroke engine through the “air passage” including the air channel 414 is charged into the scavenging channel. The air-fuel mixture produced in the air-fuel mixture channel 416 providing a part of the “air-fuel mixture passage” is induced to the crankcase of the two-stroke engine. The air-fuel mixture induced in the crankcase is compressed by the piston that is descending.
In the air leading type two-stroke engine, air accumulated in the scavenging channel at an initial stage of the scavenging process is induced into the combustion chamber and scavenging is performed by means of the air, enabling reduction of blow-by of the air-fuel mixture. As a result, HC in gas emissions can be reduced. This is a basic advantage of air leading type engines.
In an air leading type two-stroke engine, by means of respective negative pressures generated in a crankcase and a scavenging channel in the course of a piston ascending, the air-fuel mixture is charged into the crankcase and air is charged into the scavenging channel. Comparing the negative pressure exerted in the air channel 414 through the scavenging channel and the negative pressure exerted in the air-fuel mixture channel 416 through the crankcase, the negative pressure in the air-fuel mixture channel 416 is larger. In other words, the air-fuel mixture channel 416 is directly connected to the crankcase. The air channel 414 communicates with the crankcase via the scavenging channel. The negative pressure exerted in the air-fuel mixture channel 416 is directly connected to the crankcase, which is a negative pressure source, and thus, is larger and is exerted earlier than the negative pressure exerted in the air channel 414.
The relatively-large negative pressure exerted in the air-fuel mixture channel 416 draws air from the air channel 414 into the air-fuel mixture channel 416 through the opening 412 (FIG. 64). In other words, a part of the air passing through the “air passage”, that is, the air channel 414 enters the “air-fuel mixture passage”, that is, the air-fuel mixture channel 416 through the opening 412. Using this phenomenon, an engine intake quantity charged into the crankcase can be increased. This means that an engine output can be enhanced.
The relatively-large opening 412 between the two half partition members 410 positioned oppositely to each other provides a “communication portion” that brings the “air passage” and the “air-fuel mixture passage” into communication with each other in the intake system of the air leading type engine. The communication portion has the advantage as stated above. However, the existence of the communication portion has the drawback of the air-fuel mixture entering the air passage as a result of blow-back. A blow-back flow is a flow from an engine body to an air cleaner in the intake system. In other words, where a gas flow from an air cleaner to an engine body is referred to as a “forward direction”, a blow-back flow is a flow in a “reverse” direction.
Note that the terms “upstream” and “downstream” used in the present specification means upstream and downstream in a direction of a flow of gas flowing from an air cleaner to an engine body, that is, the “forward direction”, respectively.
Where a speed and amount of a first blow-back flow generated in the “air passage” in the intake system and a speed and amount of a second blow-back flow generated in the “air-fuel mixture passage” are compared, the speed and amount of the second blow-back flow in the air-fuel mixture passage leading to the crankcase having a relatively-large volume are larger. Therefore, as a result of blow-back, the air-fuel mixture in the air-fuel mixture passage enters the air passage through the communication portion. This means that the air in the air passage is contaminated. This problem hinders the aforementioned basic advantage of air leading type engines.
An object of the present invention is to provide an air leading type two-stroke engine that induces air charged in a scavenging channel of an engine body into a combustion chamber and subsequently an air-fuel mixture inside a crankcase to the combustion chamber through the scavenging channel, the two-stroke engine being capable of increasing an engine intake quantity and an engine output is thereby enhanced, and inhibiting gas emission characteristic deterioration due to blow-back, an intake system for the same and a carburetor.